This is a critical battle between two players whose shot at qualifying for the semifinals seems remote. Del Potro can blame that on his passive play against Ferrer in the first match for both men, while Tipsarevic can put it down to, well, just the fact that getting into the World Tour Finals represents a great effort on his part, but being there is apt to prove mostly that he’s in a bit over his head.

Tipsarevic played here last year as an alternate (replacing Andy Murray); this year, he’s in despite being one spot outside the Top 8, because Rafael Nadal is absent due to injury. More to the point, Tipsarevic has won just one match in this event—that one a dubious triumph over his severely depleted pal and countryman Novak Djokovic last year.

Del Potro has lost just one set in his three meetings with Tipsarevic, and it’s fairly easy to see why. Tipsarevic plays a similar, flat, first-strike game, but if they were prizefighters, the Serb would compete in a lower weight class.

A David Ferrer may be able to bamboozle a heavyweight like del Potro with great speed and defense; he can take apparent winners and send them back to extend a rally, as well as force a player like the 6’6” power baseliner to run and rush his shots more often than he likes. But while Tipsarevic is fleet and athletic, he has no great talent for working over an opponent with the equivalent of body punches. He is more likely to hit you off the court than tire you out, which is almost the exact reverse of what the doctor ordered against del Potro.

Although both men are playing for survival, del Potro’s status as a former Grand Slam champ and one-time world No. 4 is apt to arm him with a greater sense of urgency. He may have stumbled against Ferrer, and in a way that may leave him angry at himself, but he has to see this match-up as terrific opportunity to even his record at 1-1, which could put his fate back in his own hands.

One ray of hope for Tipsarevic: His U.S. Open quarterfinal with Ferrer was one of the best matches of the year (Tipsarevic lost it in a fifth-set tiebreaker). If he can be as consistent and patient against del Potro as he was in that battle, he’s got a shot.

Winner: Del Potro in two sets.

Roger Federer vs. David FerrerHead-to-head: Federer leads 13-0

Don’t believe the hype. Nor the ugly head-to-head record. Instead, be a person of true, pure, white-hot faith (which, no matter how hard you try, you can’t ever arrive at through the exercise of mere reason): Believe that Ferrer has a good chance to beat Federer in what is shaping up as the dedicated, faithful Spaniard’s career year.

Of course, man was granted reason because journalists like me are supposed to write 400-word analyses of just why this or that thing may happen, so here goes.

The men played in the round-robin stage of this event in 2010, when Federer was 29 years old. The Swiss cleaned Ferrer’s clock in that one, 6-1, 6-4. Last year, when Ferrer qualified for the single-elimination portion of the World Tour Finals, they met in the semis. Federer won it by a narrower margin, 7-5, 6-3. But it was a good sign for Ferrer that the most competitive set these two have played was the first one last year. It's easier to win a few games after a superior opponent has taken his foot off the gas; it's harder to take it to that opponent from the start.

Federer deserves all the respect in the world, but Ferrer has a surprisingly good record at the World Tour Finals—he was a finalist way back in 2007—and he's been on fire in recent weeks. He won the Valencia ATP 500 and bagged his first Masters 1000 title in Paris just last week.

This little (5’9”) guy’s fidelity to the game and all it demands is extraordinary, and at 30, Ferrer knows that whatever else his future holds, this may be his last best shot at adding some blue-ribbon titles to his nice collection of second and third-tier championships. Ferrer has won nearly half of his 18 career titles this year (seven).

And consider this: On Tuesday, Ferrer once again mastered Juan Martin del Potro (it was his third consecutive win over the big Argentine), who triumphed over Federer in the Basel final in the last match the Swiss played before the World Tour Finals. Mere chance, or are the stars aligning for Ferru?

I have always felt that one of Ferrer’s career shortcomings was a lack of vision, a tendency to be too prudent or cautious to make the most of big opportunities. But it seems like Ferrer is letting loose and rolling the dice these days, finding faith in himself. I don’t think this will be about technique or court speed or strategy or tactics; I think it will be about Federer’s age and willingness (or lack thereof) to put up with Ferrer’s relentless defense and the Spaniard’s almost desperate late-career grab at glory.